If you have an iPod (3G or 4G), buy an iTalk from Griffin. I bought one of these for my iPod to record my professors in college and it worked pretty well. It's a lot easier than lugging a laptop around.
Also, a lot of professors don't like students bringing laptops to class because a lot of students didn't pay attention. I noticed a lot of people playing solitaire or chatting on instant messenger while the lectures were taking place.